Cable operators have widely deployed high-speed data services on cable television systems. These data services allow subscriber-side devices, such as personal computers, to communicate over an ordinary cable TV network Hybrid Fiber Coax (HFC) cable. A Cable Modem Termination System (CMTS) connects the cable TV network to a data network, such as the Internet. The Data Over Cable Service Interface Specification (DOCSIS) is one of the cable modem standards used for transferring data over the cable TV network.
In a DOCSIS network, the data traffic is classified by specified fields in the data packet headers into service flows (also referred to as flows, sessions, etc. in non-DOCSIS networks), and a scheduling device in the CMTS regulates the packet transmission based on the pre-defined Quality of Service (QoS) parameters associated with the service flows. Examples of the QoS parameters include relative traffic priority, minimum reserved bandwidth, maximum sustained bandwidth, etc. In the downstream direction, the physical transmission of packets is over physical Radio Frequency (RF) channels to the cable modems. Each RF channel has fixed amount of bandwidth based on its modulation characteristics.
In the latest DOCSIS version, version 3.0, each service flow can be transmitted over a single one of the RF channels (non-bonded, also called narrowband), or distributed over a plurality of the RF channels (bonded, also called wideband). Consequently, an RF channel can be used to carry a plurality of narrowband transmissions and/or a plurality of portions of wideband transmissions.
Since a same RF channel can be used to carry a plurality of narrowband transmissions and/or a plurality of portions of wideband transmissions, the CMTS uses a scheduling scheme to keep the transmitted data rate within the maximum transmission rate of the RF channel. Existing scheduling schemes leave a significant portion of available RF channel bandwidth unused under certain circumstances even though buffered data is waiting for transmission on the CMTS. The disclosure that follows solves this and other problems.